1. Field of the Invention
This invention relates to the preparation of alkali metal and other water soluble salts of carboxymethyloxy succinic acid from maleic acid and glycolic acid.
2. Description of the Prior Art
Carboxymethyloxy succinic acid and its water soluble salts have utility as builders as disclosed in U.S. Pat. No. 3,914,297 which also discloses a preferred method of preparing such materials by reacting maleic acid and glycolic acid in the presence of zinc or alkaline earth metal ions to form zinc or alkaline earth metal salt of carboxymethyloxy succinic acid and then treating such zinc or alkaline earth metal salt to convert it into the desired water soluble salt. Typically, in the treating operation as performed in the prior art sodium carbonate is added to the zinc or alkaline earth metal salt to produce trisodium carboxymethyloxy succinate and by-product zinc or alkaline earth metal carbonate, the latter in the form of a precipitate which must be removed to provide a solution from which the trisodium carboxymethyloxy succinate can be recovered. Unfortunately the removal of the by-product carbonate salt is very difficult when attempted as described in the process of U.S. Pat. No. 3,914,297. Alleviation of the difficulty is sought as described in U.S. Pat. No. 3,821,296 which uses a "heel" of trisodium carboxymethyloxy succinate in the reaction of calcium carboxymethyloxy succinate and sodium carbonate. It would be desirable to provide a suitable treating process which does not require the use of a "heel."